An optical element includes an optical anisotropic medium. A difference between a minimum refractive index nl and a maximum refractive index nh of the optical anisotropic medium at a used central wavelength is at least 0.1, and a refractive index nt1 of a first medium optically adjacent to the optical anisotropic medium at the used central wavelength satisfies the following condition: (nt1−nl)·(nt1−nh)≦0.